The present disclosure generally relates to a sensor device for use in a medical fluid delivery system and, in particular, to an infusion pumps device, like an insulin infusion pump device, to monitor a fluidic pressure and/or detecting occlusions in a fluidic system of such system and device.
Medical fluid delivery systems for the administration of, for example, liquid medical fluids, such as infusion pump devices, are often used with patients who have a continuous, and in the course of the day varying, need of a medicine that can be administered, for example, by subcutaneous infusion. Specific applications are, for example, certain pain therapies and the treatment of diabetes. In such cases, computer controlled automated infusion pump devices are used, which can be carried by the patient on the body, and which contain a certain amount of liquid medicine in a medicine reservoir. The liquid medicine is supplied to the patient's body from the medicine reservoir through a fluidic system to an infusion cannula or an injection needle. Mostly such medical fluid delivery systems comprise a reusable unit including an actuation mechanism, a dosing mechanism, electronics for controlling the mechanisms, and the like and a disposable unit including, for example, a fluid reservoir, which is discarded after emptying the reservoir.
The liquid medicine can be obtained by a downstream pump from a flexible container. Flexible containers have the advantage of a smaller volume surplus of the container in relation to its content reducing the manufacturing costs and enabling design of infusion pump devices of smaller overall dimensions. Thus, the device cannot be seen through clothing and can be carried as comfortably as possible.
In the context of liquid medicine administration via an infusion pump device, sensor devices are used for controlling the dosing, monitoring the correct operation of the system, and for fast detection of faults and hazards, such as occluded infusion lines or cannulae, empty containers, or malfunctioning pump systems. A pressure sensor device may be in a fluid path downstream of a pump device and upstream of an infusion cannula.
Such pressure sensor devices typically comprise a micro-fluidic chamber filled with liquid and fluidly connected to the fluidic system. The chamber is covered by a flexible, resilient membrane such that a pressure difference between the fluidic pressure inside the sensor chamber and the outside (such as atmospheric) pressure will temporarily deform the membrane. The resulting deflection of the membrane can then be measured in order to determine the internal pressure of the fluidic system.
A suitable approach to measure the deformation of the membrane is optical detection of a light beam reflected on the membrane. The pressure sensor device includes a micro-fluidic chamber connected to a fluidic system comprising a rigid bottom substrate and a flexible, resilient top cover, for example, a membrane. An optical detection system measures a deformation of the cover membrane by determining the interaction of a light beam with the cover membrane. For that purpose, a light emitting device, such as, a laser diode, directs a light beam at a certain angle onto the surface of the cover membrane where it is reflected. The pressure difference between the inner volume of the micro-fluidic chamber and the outer environment acts on the cover membrane and deforms it to a certain extent depending on the pressure difference. As a result, the angle of the reflected light beam changes and the beam is transversely shifted. By monitoring the position of the reflected light beam, the deformation of the cover membrane can be measured and based on the obtained results a pressure difference value can be determined.
In one example, an insulin pump comprises a reusable unit with drive, dosing and controlling systems and a disposable unit with a flow path and a catheter tube. The flow path can be connected to the driving and dosing mechanism such that a liquid system runs from a liquid reservoir to the catheter tube. A resilient membrane is in the flow path and covers a fluidic chamber. The membrane is impinged directly by the liquid in the flow path such that it is deflected towards the reusable unit in case of a pressure increase, for example, due to an occlusion of the liquid system. The reusable unit comprises a light emitter in form of a laser diode and a photosensitive x-y sensor connected to the controlling system. The light beam of the laser diode can be directed on a rigid reflector arranged on the membrane. Alternatively, the light beam can be directed directly on the membrane surface. In this case, a small area on the surface of the membrane is metal-coated to provide good reflecting properties of the membrane. The incident light beam is focused on an area of the membrane at a distance to the center of the membrane. That means in a deflected state of the membrane the reflecting area is inclined and rounded with respect to the non-deflected state. Therefore, a reflected light beam changes direction and shape, which can be detected by the x-y sensor and is an indication for a pressure change within the liquid system.
Another infusion pump system comprises an occlusion sensor that can be used to detect when an occlusion exists in the fluid path between a medicine reservoir and the infusion site. The occlusion sensor includes a flexible membrane which can be deflected by rising pressure in the fluid path such that it touches a wall of an air cavity. The incident measurement light beam is guided through a light transmissive member to the air cavity. In a non-deflected state, the incident beam is totally reflected at the air cavity. In a deflected state, when the membrane touches the air cavity, reduced reflection occurs. The reduction of the intensity of the reflected light beam is a measurement for the pressure in the fluid path.
Since some of the parts of the pressure sensor device are in the disposable unit and other parts are in the reusable unit, the orientation of disposable and reusable part towards each other can be a critical parameter of reliable measuring results. In the known systems, the tolerances between these units must be as small as possible. For monitoring the reflected light beam in a pressure sensor according to the prior art, a detector in the optical detection system often is designed to be movable, or a multiplicity of detectors at different positions and at different angles are included in the device. Both of these aspects make such sensor devices expensive and difficult to make. A wide range of directions of reflected light beams due to the large variety or diffuse reflection angles on a membrane also requires a complex sensor array in the pressure sensor device.
Therefore, there is a need to provide an improved sensor device for use in a medical fluid delivery system, such as an infusion pump device for liquid medicines, like insulin, for monitoring pressure variations in a medical fluid delivery system, which is easy to install and indicates pressure changes or fluid path occlusion in a simple manner and overcome the drawbacks of prior art devices.